手性亚磷酰胺配体及其在不对称催化中的应用

由于结构稳定、合成简便、修饰容易、效果独特等优点,手性亚磷酰胺配体在近十几年得到了迅速的发展,大量基于不同骨架的配体被开发出来,并被成功地应用于多种不对称催化反应中.主要综述了该类配体在不对称共轭加成和烯丙基取代反应中的研究进展,同时也简单介绍了该类配体在其它不对称催化反应中的最新应用.     

On the Frontier Between Nucleophilic Aromatic Substitution and Catalysis

A study on the arylation of heteroatom nucleophiles by using activated haloarenes, with or without metal catalysts, is reported. A discussion concerning the involvement of traces of metals is presented, supported by an unexpected ''ligand'' effect in the absence of added metal catalysts. We believe that the frontier between nucleophilic aromatic substitution and catalysis will likely prove to be much harder to delimit than is generally thought.     

The Effectivity of 1H‐Triazoles and ‐Tetrazoles as Activators in Acid‐Catalyzed Phosphoramidite Alcoholysis

The efficiency of 5‐nitro‐1,2,4‐1H‐triazole ( 3 ), 5‐(methylthio)‐1H‐tetrazole ( 4 ), and 5‐(4‐nitrophenyl)‐1H‐tetrazole ( 5 ) as activators in phosphoramidite alcoholysis has been studied relative to 1H‐tetrazole ( 6 ). Reactions of these azoles with diisopropyl (diisopropylamido)phosphite ( 1a ) were followed in THF, and the rates were found to increase with increasing acidity of the azoles. The Brønsted α value of 0.7 determined for this dependence is in agreement with data published earlier.     

Re-examination of Nucleophilic Substitutionin Chlorokojic Acid

 Chlorokojic acid was reacted with S₂O₃ ²⁻, NO₃ ⁻, N₃ ⁻, I⁻, and SCN⁻. Only the three latter nucleophiles substituted the chlorine atom in the 2-CH₂Cl group of kojic acid. In none of the products nucleophilic substitution at position 6 of the 4-pyrone could be found. Regular substituion of chlorokojic acid with I⁻ (iodokojic acid), N₃ ⁻ (azidokojic acid), and SCN⁻ (thiocyanato and isothiocyanato kojic acids) was accompanied by formation of allomaltol. Reaction pathways for the formation of allomaltol and 6-substituted allomaltol derivatives are proposed. The latter has been formerly discovered in the reaction of chlorokojic acid with secondary amines.     

Re-examination of Nucleophilic Substitutionin Chlorokojic Acid

Summary.  Chlorokojic acid was reacted with S₂O₃ ²⁻, NO₃ ⁻, N₃ ⁻, I⁻, and SCN⁻. Only the three latter nucleophiles substituted the chlorine atom in the 2-CH₂Cl group of kojic acid. In none of the products nucleophilic substitution at position 6 of the 4-pyrone could be found. Regular substituion of chlorokojic acid with I⁻ (iodokojic acid), N₃ ⁻ (azidokojic acid), and SCN⁻ (thiocyanato and isothiocyanato kojic acids) was accompanied by formation of allomaltol. Reaction pathways for the formation of allomaltol and 6-substituted allomaltol derivatives are proposed. The latter has been formerly discovered in the reaction of chlorokojic acid with secondary amines. Received October 10, 1999. Accepted (revised) November 25, 1999     

Nitrenium Salts in Lewis Acid Catalysis

Molecular compounds featuring nitrogen atoms are typically regarded as Lewis bases and are extensively employed as donor ligands in coordination chemistry or as nucleophiles in organic chemistry. By contrast, electrophilic nitrogen‐containing compounds are much rarer. Nitrenium cations are a new family of nitrogen‐based Lewis acids, the reactivity of which remains largely unexplored. In this work, nitrenium ions are explored as catalysts in five organic transformations. These reactions are the first examples of Lewis acid catalysis employing nitrogen as the site of substrate activation. Moreover, these compounds are readily accessed from commercially available reagents and exhibit remarkable stability toward moisture, allowing for benchtop transformations without the need to pretreat solvents.     

Alkynes as Electrophilic or Nucleophilic Allylmetal Precursors in Transition‐Metal Catalysis

Diverse late transition metal catalysts convert terminal or internal alkynes into transient allylmetal species that display electrophilic or nucleophilic properties. Whereas classical methods for the generation of allylmetal species often form stoichiometric by‐products, the recent use of alkynes as allylmetal precursors enables completely atom‐efficient catalytic processes to be carried out, including enantioselective transformations.     

Highly Enantioselective Nucleophilic Dearomatization of Pyridines by Anion‐Binding Catalysis

The asymmetric dearomatization of N‐heterocycles is an important synthetic method to gain bioactive and synthetically valuable chiral heterocycles. However, the catalytic enantio‐ and regioselective dearomatization of the simplest six‐membered‐ring N‐heteroarenes, the pyridines, is still very challenging. The first anion‐binding‐catalyzed, highly enantioselective nucleophilic dearomatization of pyridines with triazole‐based H‐bond donor catalysts is presented. Contrary to other more common NH‐based H‐bond donors, this type of organocatalyst shows a prominent higher C2‐regioselectivity and is able to promote high enantioinductions via formation of a close chiral anion‐pair complex with a preformed N‐acyl pyridinium ionic intermediate. This method offers a straightforward and useful synthetic approach to chiral N‐heterocycles from abundant and readily available pyridines.     

Nucleophilic and Electrophilic Activation of Non‐Heteroaromatic Amides in Atom‐Economical Asymmetric Catalysis

Recent advances in catalytic asymmetric carbon–carbon bond‐forming reactions of non‐heteroaromatic amide substrates are highlighted. Among carbonyl compounds, amides have received limited attention in catalytic asymmetric transformations mainly owing to their lower reactivity. Amides are reluctant to form enolates for nucleophilic addition, and α,β‐unsaturated amides exhibit diminished electrophilicity at the β‐carbon. Recent advances in asymmetric catalysis rendered these amides amenable to enantioselective reactions with perfect atom economy, producing synthetically useful chiral building blocks. This Minireview summarizes recent developments in the field.     

2H-吡咯的简易合成方法:金催化与路易斯酸催化的组合应用

报道了利用金催化与铜催化相结合合成5-氨基-2H-吡咯的方法. 首先通过均相金催化异恶唑与炔酰胺反应生成α-亚胺金卡宾中间体, 再经[3+2]环加成反应合成并分离出5-氨基-3H-吡咯, 然后通过铜催化的去酰基化和基团迁移反应来实现3H-吡咯向2H-吡咯的转化. 该方法不但操作简单、反应条件温和、官能团兼容性良好, 而且还能进行克量级放大. 这项研究为合成具有重要生物活性的5-氨基-2H-吡咯化合物提供了广谱实用的合成方法.     

Asymmetric Synthesis of Stereogenic Phosphorus P(V) Centers Using Chiral Nucleophilic Catalysis

Organophosphates have been widely used in agrochemistry, as reagents for organic synthesis, and in biochemistry. Phosphate mimics possessing four unique substituents, and thereby a chirality center, are useful in transition metal catalysis and as nucleotide therapeutics. The catalytic, stereocontrolled synthesis of phosphorus-stereogenic centers is challenging and traditionally depends on a resolution or use of stochiometric auxiliaries. Herein, enantioenriched phosphorus centers have been synthesized using chiral nucleophilic catalysis. Racemic H-phosphinate species were coupled with nucleophilic alcohols under halogenating conditions. Chiral phosphonate products were synthesized in acceptable yields (33–95%) and modest enantioselectivity (up to 62% ee) was observed after identification of an appropriate chiral catalyst and optimization of the solvent, base, and temperature. Nucleophilic catalysis has a tremendous potential to produce enantioenriched phosphate mimics that could be used as prodrugs or chemical biology probes.     

Nucleic Acid Catalysis under Potential Prebiotic Conditions

Catalysis by nucleic acids is indispensable for extant cellular life, and it is widely accepted that nucleic acid enzymes were crucial for the emergence of primitive life 3.5‐4 billion years ago. However, geochemical conditions on early Earth must have differed greatly from the constant internal milieus of today's cells. In order to explore plausible scenarios for early molecular evolution, it is therefore essential to understand how different physicochemical parameters, such as temperature, pH, and ionic composition, influence nucleic acid catalysis and to explore to what extent nucleic acid enzymes can adapt to non‐physiological conditions. In this article, we give an overview of the research on catalysis of nucleic acids, in particular catalytic RNAs (ribozymes) and DNAs (deoxyribozymes), under extreme and/or unusual conditions that may relate to prebiotic environments.     

Acid Catalysis in Reaction of Ozone with Chloride Ions

The kinetics of the interaction of ozone with aqueous solutions of chlorides resulting in Cl₂ evolution to the gas phase was studied. The reaction of O₃ with Cl^– is accelerated by H⁺ ions. The effects of the concentrations of H⁺ and Cl^–, the ionic strength, and temperature (ranged from 7 to 60°C) on the reaction rate were studied. A mechanism explaining the experimental kinetics was proposed. The acid catalysis is due to the formation of the HO₃Cl complex, which is in equilibrium with H⁺, O₃, and Cl^–. The constants of reactions involved in the proposed mechanism were determined.     

Phosphoramidite ligands in iridium-catalyzed allylic substitution

A new phosphoramidite ligand was used in the iridium-catalyzed allylic substitution reaction. This permitted high regio- and enantioselectivities on a wide variety of substrates and nucleophiles. Because of the stereospecificity of the reaction obtained by using branched substrates, a kinetic resolution reaction was attempted. The origin of the impressive efficiency of this ligand in terms of kinetics was explored in detail, as was the role of the substituent in the ortho-position of the amine moiety.     

Nucleophilic Aromatic Substitution of Unactivated Aryl Fluorides with Primary Aliphatic Amines by Organic Photoredox Catalysis

In this work, a mild and transition-metal-free approach for the nucleophilic aromatic substitution (S_NAr) of unactivated fluoroarenes with primary aliphatic amines to form aromatic amines is reported. This reaction is facilitated by the formation of cationic fluoroarene radical intermediates in the presence of an acridinium-based organic photocatalyst under blue-light irradiation. Various electron-rich and electron-neutral fluoroarenes are competent electrophiles for this transformation. A wide range of primary aliphatic amines, including amino acid esters, dipeptides, and linear and branched amines are suitable nucleophiles. The synthetic utility of this protocol is demonstrated by the late-stage functionalization of several complex drug molecules.     

铌酸/氧化铌在多相催化反应中的应用

介绍了铌酸，氧化铌的结构、性质及其在多相催化反应中的研究现状及应用前景。作为一种新型的催化材料，铌酸，氧化铌由于其独特的酸性和氧化还原性正受到越来越多人的关注。它可以作为催化剂的活性组分、助剂或载体使用，在烃类转化、选择性氧化、水解、水合、缩合、加氢，脱氢等若干酸碱和氧化还原反应中得到广泛的应用。